Introduction
Structural engineers have to balance their load-bearing structure designs to be economical and safe. Nowadays, they need to deal with more and more slender concrete columns and other subtle structures either to save costs or to satisfy architectural requirements. This is even more highlighted in prefabricated structures where components are designed to be exceptionally slender, aiming to reduce weight and maximize material efficiency. However, a critical question arises: how can we ensure the stability of slender concrete columns, while maintaining both economic feasibility and safety in the design? The answer is that it can be approached in several ways:
One could engage in manual, albeit laborious, calculations or employ simpler tools like Excel spreadsheets. A more efficient alternative is IDEA StatiCa Member, a software that has been designed to streamline these calculations in their more advanced form.
What is IDEA StatiCa Member?
IDEA StatiCa Member is a sophisticated software application developed to address stability challenges in steel & concrete sub-structures. It facilitates easy modelling of the structural system, application of all relevant loads, reinforcement design, and immediate execution of analyses and checks. It could also extract these sub-structures from a global analysis software under equilibrium and transform them into detailed models with precise boundary conditions.
More importantly, IDEA StatiCa Member incorporates advanced analytical methods that were traditionally limited to academic research. These methodologies are now streamlined, allowing structural engineers to apply them within realistic timeframes, transforming complex analyses from a lengthy process to a more manageable task.
Code Limitations for the Design of Slender Columns
Designing slender concrete columns, can be quite complex. Factors such as imperfections and second-order effects significantly influence design internal forces and must be accurately considered to ensure structural safety and efficiency.
The process of defining slenderness limits and adhering to code provisions for slender members involves numerous assumptions, including determining effective length based on structural behaviour and the stiffness and position of lateral supports. The application of calculated imperfections, particularly in biaxial bending, adds to this complexity.
Eurocode provision §5.7.(5) recognizes these challenges and permits the use of advanced non-linear design methods for slender members where second-order effects are significant.
IDEA StatiCa Member to the Rescue
To circumvent the limitations and conservative approaches often necessitated by code, IDEA StatiCa Member leverages the general design method specified in §5.8.6. This method includes a geometrically non-linear analysis that incorporates second-order effects. Material non-linearity is addressed through stress-strain material laws based on design values.
IDEA StatiCa Member ensures accurate boundary conditions by considering laterally supporting members, their loads and internal forces. This comprehensive approach fulfils the code’s requirements for equilibrium and strain compatibility.
Using IDEA StatiCa Member, engineers can efficiently determine buckling lengths through a Linear Bifurcation Analysis (LBA), easily initiated with a single click. The critical buckling length is identified and amplified according to code values, followed by a GMNIA analysis that includes geometric non-linearities. Upon completion, the software conducts detailed concrete and reinforcement checks at each section of the member under the amplified internal forces, presenting results comprehensively, and allowing engineers to identify and address critical areas effectively.
Conclusion
With IDEA StatiCa Member, engineers no longer need to default to conservative designs when dealing with slender concrete columns. This tool empowers designers to maximize the potential of their reinforced concrete structures through a streamlined and efficient workflow. Its compatibility with popular global analysis software (like SAP2000, Robot, SCIA Engineer, AxisVM, etc) enhances its utility, allowing for the seamless integration and updating of designs in response to changes in the global analysis model. IDEA StatiCa Member, represents a significant step forward in the optimization of slender concrete column design.
Costis Hatzopoulos
Technical Director, IDEA StatiCa UK